In the manufacture of many useful articles, such as furniture, it is often desirable to provide for angled corners. Such corners are typically right angles, as at the intersection of the sides and front or back of a cabinet, but maybe obtuse or acute angles. Also, furniture pieces often have protrusions, such as in the front surface of the countertops. Generally, such angles are formed by abutting and joining two panels of a base material, by dovetailing the panels, by miter and doweling, or by external bracing. Generally, protrusions have a front edge which is at a right angle to the top and bottom surfaces. The formation of angles by joining results in sharp corners which may be undesirable. As a result, in certain applications, such as furniture used in the food industry, round corners are preferred. Rounded corners are easier to clean than are angled corners, and pose less of a danger to children and other individuals who might bump into the corner.
Techniques for obtaining rounded corners in wood articles are known in the prior art. Rounded corners are obtained by bending a sheet of material to obtain the desired angular bend. Various techniques for bending wood and making articles from bent wood have been disclosed in Pine, U.S. Pat. No. 230,457; Rogers, U.S. Pat. No. 693,323, Clark, U.S. Pat. No. 709,204; Basquin, U.S. Pat. No. 1,346,161; and Sabo, U.S. Pat. No. 4,236,558.
Pine discloses a technique for bending wood in which a rectangular or semi-circular cutout is made partially through a length of wood, leaving a thin connecting strip. The wood is then bent around a template placed inside the cutout to produce a bend in the wood at the cut. In the method of Pine, a right-angled corner results which is a point of structural weakness. The corner is either formed by the template which produces a multi-angled interior, when a rectangular cutout is used, or by the tangent of the circular opening.
Rogers discloses a chair made from a single piece of wood that is bent to provide the various parts of the chair, including the seat, back and arms. Bends in the wood are formed by cutting away the major portion of the wood stock to form a thin, bendable web. Arm and leg elements form an elliptical solid portion within the bend at the front of the seat.
Clark discloses a method for bending wood that is similar to that of Pine. Clark differs from Pine in that the cut in the length of wood and the template are rounded at their internal and external extremities, respectively, to eliminate a point of structural weakness in the bend, and the inner portion of the template is cut to provide a single right angle at the interior of the bend.
Basquin discloses a method for bending plywood in which the innermost ply is removed at the desired portion so that the remaining next innermost ply has its grain extending lengthwise perpendicular to the direction of the bend. The result is a bend with decreased thickness of wood compared to the wood on either side of the bend. This provides a point of structural weakness in the bend.
Sabo discloses a method for making a 90 degree corner with a rounded socket. A rounded oblong cut is made in the length of wood. The wood is cut at a 45 degree angle obliquely to the lateral inner surface of the circular portions to result in a closed circular socket when the wood is bent. The wood is steamed to provide flexibility for bending. The socket provides an opening for introducing an elongate circular element, such as a chair leg. The corner is locked in place by using a dowel that is inserted in matching holes between the circular opening and the inner surfaces of the angle.
Bending wood sheets that are covered with plastic laminate is much more difficult. In order to bend a laminate, it must first be heated to make it bendable. However, when the laminate is heated it becomes soft and must be supported during the bending process. Furthermore, when a wood sheet with plastic laminate is bent, the laminate tends to be stretched, since it is at the outside of the bend.
Owens, U.S. Pat. No. 2,081,638 discloses a method of bending solid or laminated boards in which a rectangle with rounded ends is cut into the board to leave a bendable web having the thickness of the veneer or of the veneer and a thin portion of the underlying wood. A layer of veneer is glued to the inside of the cut and a heated circular die is positioned on this layer of veneer. The board is then bent at the web around the die to result in a bend with a veneer coating on its inner side. Owens does not address the problem of stretching that occurs during bending.
A first preferred embodiment of the subject invention provides a method for bending a sheet of wood having a plastic laminate on its outside face to form a rounded corner. A cut which opens out of the inside face of the sheet is made across the sheet at the line of the corner. This cut forms a gap in the inside face of the sheet. The cut has a cross-sectional shape that will cause it to close into an elongate, circular, cylindrical opening having a predetermined diameter with the gap being substantially closed, when the sheet is bent to its desired angle. The plastic laminate is then heated to make it bendable. A circular cylindrical dowel with the same predetermined diameter having adhesive applied to it is placed in the cut in the sheet. The sheet is then bent around the dowel until the sheet completely surrounds the dowel and the sheet is held in place until the laminate cools and the adhesive cures.
A second preferred embodiment of the invention provides an apparatus for bending a sheet of laminate-covered wood according to this method. A first platform engages the outside face of the sheet of material on one side of the cut. A second platform engages the outside face of the sheet on the other side of the cut. A mechanism rotates the first platform while simultaneously translating it toward the cut in a manner in which the laminate is not stretched while the sheet is being bent.
In one preferred embodiment, this mechanism includes a rack, which is attached to and movable with, the second platform, and a pinion which engages the rack and is not movable with the second platform. The pinion is located so that its center line is coaxial with the center line of the dowel when the sheet is bent around it.
The apparatus also provides a heater for heating the laminate before bending, and a spindle for rotatably carrying the dowel and placing it in the cut. The apparatus also includes an adhesive gun for applying adhesive to the dowel before it is placed on the cut. The apparatus also includes a dowel heater for preheating the dowel before the adhesive is applied.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.